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1.
王志翠  何伦华  王海  刘荣灯  王芳卫 《中国物理 B》2012,21(4):46101-046101
The crystallographic structure and magnetic properties of La(Fell.4Alz.6)C0.02 are studied by magnetic measurernent and powder neutron diffraction with temperature and applied magnetic field. Rietveld refinement shows that La(Fe11.4Al1.6)C0.02 crystallizes into the cubic NaZn13-type with two different Fe sites: FeI (8b) and FeII (96i), and that A1 atoms preferentially occupy the FeII site. A ferromagnetic state can he induced at a medial temperature of 39 K-139 K by an external magnetic field of 0.7 T, and a large lattice is correspondingly found at 100 K and 0.7 T. In all other conditions, La(Fe11.4Al1.6)C0.02 has no net magnetization in the paramagnetic (T 〉 TN = 182 K) or antifer- romagnetic states, and thus keeps its small lattice. Analysis of the Fe Fe bond length indicates that the ferromagnetic state prefers longer Fe-Fe distances.  相似文献   
2.
Hydrogenation, crystal structure and magnetic properties of La(Fe0.91Si0.09)13H(D)y have been studied by pressure-composition isotherms (PCI), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and magnetization measurements. The maximum absorption capacity is found to be 1.9 H(D) atoms per formula unit as a solid solution. All hydrides and deuterides crystallize in the NaZn13-type cubic structure with the lattice parameter increasing linearly with H(D) concentration. The H(D) absorption enhances the Curie temperature significantly. The magnetic entropy change of the highly H-absorbed compound La(Fe0.91Si0.09)13H1.81 reaches ~26 J/kg·K under a magnetic field change of 5 T near the Curie temperature TC = 350 K. No observable isotope effect seems to imply that only the magnetovolume effect is responsible for the strong interplay between magnetism and lattice.  相似文献   
3.
Co掺杂的ZnO稀磁半导体块体的退火热处理研究   总被引:1,自引:0,他引:1       下载免费PDF全文
彭先德  朱涛  王芳卫 《物理学报》2009,58(5):3274-3279
采用固相反应法制备了Zn0.95Co0.05O块体样品,并对其进行了不同方式的退火处理.实验表明在锌气氛中500℃退火的样品表现出铁磁性,而在真空中退火的样品却没有磁性,进一步,在锌气氛中1100℃退火的样品虽然表现出铁磁性,但其铁磁性来源于样品在锌气氛中1100℃退火过程中产生了1%左右的Co金属团簇杂质相.另外,在低温时所有样品都表现出较大的正磁电阻,认为正磁电阻效应是由于s-d电子交换相互作用引起的自旋劈裂造成的,而高场时出现的负磁电阻效应则可能归因于磁场 关键词: Co掺杂ZnO X射线衍射 铁磁性 磁电阻  相似文献   
4.
曹慧波  何伦华  王芳卫 《中国物理》2005,14(9):1892-1895
A new single-molecule magnet [Mn11Fe1O12 (CH3COO)16(H2O)4]?2CH3COOH?4H2O (Mn11Fe1) has been synthesized.The structure has been studied by the single crystal x-ray diffraction. The difference of Jahn--Teller distortion between Fe3+ and Mn3+ ion reveals that Fe3+ ion substitutes for Mn3+ ion on the Mn(3) sites in the Mn12 skeleton. The temperature dependence of the magnetization gives a blocking temperature TB=1.9K for Mn11Fe1. Based on the magnetization process analysis of the crystal at T=2K, we suggest that Mn11Fe1 has the ground state with a total spin S= 11/2.  相似文献   
5.
张绍英  王芳卫 《物理》2005,34(10):774-774
散裂中子源是基于质子加速器产生的高能质子轰击重金属靶造成重金属原子散裂从而提供高脉冲中子通量的平台型大科学装置,散裂中子源在众多学科领域,特别是物质科学领域得到了广泛的应用,结合目前正在筹备阶段的北京散裂中子源(BSNS)项目的“第二届散裂中子源多学科应用研讨会”于2005年7月27日—29日在北京中国科学院物理研究所召开。  相似文献   
6.
第一讲中子散射与散裂中子源   总被引:1,自引:0,他引:1  
中子散射是研究物质微观结构和动态的理想工具之一,广泛地应用于凝聚态物质研究和应用的众多学科领域.散裂中子源能是新一代的加速器基脉冲中子源,能为中子散射提供高通量的脉冲中子.文章简明地介绍了中子散射的特点和它作为物质结构和动态探针的优越性,以及散裂中子源的基本原理、发展状况和多学科的应用优势.我国计划建设的散裂中子源CSNS中,靶站将由多片钨靶、铍/铁反射体和铁/重混凝土生物屏蔽体组成.质子束功率100kW下,脉冲中子通量约为2.4×1016n/cm2/s.第一期将设计建造高通量粉末衍射仪、高分辨粉末衍射仪、小角散射仪、多功能反射仪和直接几何非弹性散射仪等五台典型的中子散射谱仪,以覆盖大部分的中子散射研究领域.  相似文献   
7.
We report on alloys formed by replacing iron with manganese in the compound Dy2Fe17C1.0 Samples were characterized by X-ray diffraction and magnetic measure-ments, The 2:17-type structure can be crystallized in the whole range of manganese substitution. The Curie temperature of the series of Dy2Fe17-xMnxC1.0(x= 0-17) drops down considerably from 515K for x = 0 to about 20K for compounds with high manganese concentration, and the compensation point was observed in a narrow range of x≈4-6. The rapid decrease of the magnetization shows that the manganese substitution is not a simple magnetic dilution to the transition-metal sublattice mo-ment, it indicates that the moment of Mn may be antiparallel to that of Fe. The field dependence of the magnetization of Dy2Fe17-xMnxC1.0 may indicate the existence of the nonlinear magnetic structure for the samples with high Mn conoentrations.  相似文献   
8.
 历史上每一次人类社会的重大进步都伴随着能源的变革。化石能源的利用给人类社会带来极大便利的同时,也对我们赖以生存的自然环境造成了巨大破坏,发展绿色、清洁、高效的可替代能源是当代科技工作者肩负的重要使命。当前,各国都在加大对核能、太阳能、风能、生物能、水能等清洁能源的开发力度,大量的人力和物力投入到这一能源变革之中。  相似文献   
9.
王海霞  殷雯  王芳卫 《中国物理 B》2010,19(3):30308-030308
Using the method developed by Gurvitz [1996 Phys.Rev.B 53 15932],we obtained the Bloch-type rate equations describing the entire system of a periodically driving qubit monitored by a quantum point contact detector.The results demonstrate that the isolated qubit can be kept in its initial state with a large driving frequency due to more difficult electron tunneling in qubit,and this initial state can always be measured at a small measurement-induced decoherence rate during a short time.  相似文献   
10.
The quantum tunnelling of magnetization (QTM) in single crystals of the single molecule magnet (Mn1-xCrx)12- Ac (x=0, 0.03, 0.04, 0.05) has been investigated. In comparison with its parent Mnl2-Ac, a greater rate of magnetization relaxation and a lower effective potential-energy barrier have been observed in Cr-doping samples. This modulation of QTM due to the Cr-doping could be attributed to the small change of Sz due to the smaller spin of Cr itself and additional intrinsic but distributed transverse and longitudinal anisotropy raised by a subtle change of the local environment in the magnetic Mn12 core.  相似文献   
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